1. Field of the Invention
The present invention relates to a vertical deflection circuit for yokes of kinescopes, with improved flyback generator, particularly for high-definition monitors and kinescopes.
2. Prior Art
As is known, to rapidly reverse the current in the vertical deflection yoke of a cathode-ray tube during flyback, higher voltages than that applied during the scanning period, which is approximately equivalent to the yoke current (I.sub.pp) multiplied by the impedance of the load, are generally required.
To generate this voltage while keeping the average power dissipation low, the Italian patent No. 992.626 in the name of the Applicant proposed a circuital solution, adopted in almost all vertical deflection circuits, constituted by a voltage doubling circuit, employing the charge of an electrolytic capacitor, which allows to apply twice the supply voltage to the vertical deflection coil only for the return period, during which the rapid reversal of the current is required.
This prior solution is adequate for kinescopes of commercial television sets, since a voltage equal to twice the minimum value is sufficient to reverse the current in a time shorter than the vertical blackout time tB, which is usually approximately equal to 1.4 msec.
Instead, in application to monitors, particularly of the high-definition type, where the vertical blackout time must be shorter than 0.5 msec (both due to the reduction of the frame time and because it is desired to employ the visualized area to its optimum), the ratio between the flyback V.sub.f, which minimizes the return time, and the minimum supply V.sub.s, which corresponds to the minimum power dissipation, must be of the order of V.sub.f /V.sub.s =3.div.4.
For this reason, the flyback voltage generator of said antedated patent is no longer adequate (V.sub.f /V.sub.s =2).